Ford Capri RS3100


Ford Capri RS3100
1973 - 1974
Country:
Engine:	6 cyl.
Capacity:	3091 cc
Power:	148bhp @ 5000rpm
Transmission:	4 Speed Manual
Top Speed:	201 kmh
Number Built:	50 (Aust. Imports)
Collectability:

Ford Capri RS3100
Reviewed by Unique Cars and Parts
Our Rating: 5

Introduction

In November 1973, at Ford's Halewood plant in the UK, production of the RS3100 began. Production of the RS3100 actually overlapped with the Capri MKII and was intermittent at best. Homologated in January 1974 for the forthcoming UK Touring Car season, only 248 examples of the RS3100 were officially completed. They were an expensive road car at 2,450 Pounds and arrived right in the middle of the 1970's oil crisis.

Ford Australia managed to import 50 examples of this "Special" Capri and many of these cars still exist today in private collections. These examples sold in Australia for $6,250.00 The RS3100 differed from the 3000GT with a larger bore and therefore an increase in capacity to 3091cc (188.6 cu in), a Weber 38 EGAS twin choke carburettor and a 9.0:1 compression ratio, which meant it developed 148bhp @ 5000rpm.

Its torque was rated at 187lb ft @ 3000rpm and it came with manual transmission only, with an optional limited slip differential. It had ventilated disc brakes, RS2600 German cast alloy wheels with 6in wide rims and had a top speed of 125mph (201kmh). 1973 had not been a good year for Ford in the European Touring Car championship. After two years at the top the highly acclaimed RS2600 had finally been overcome by BMW's 3.0 litre CSL. One of the major advantages that the CSL had over the RS2600 was its improved aero dynamics.

Nicknamed the "batmobile" due to its new wings the CSL knocked 15 seconds off the previous lap times at the Nurburgring, and was signigicantly more stable to drive. In order to redress the balance Ford needed a new contender. This was to be the RS3100. To improve the aerodynamics of their racing Capri's Ford fitted newly designed front and rear spoilers. To meet the ETC rules these new aerodynamic aids on the racing RS3100's had to have been fitted to 100 road homologation cars. The distinctive boot mounted "duck-tail" rear spoiler and smaller front lip spoiler reduced the coefficient of drag (Cd) from 0.40 on the RS2600 to 0.37 for the RS3100.

The RS2600 had used the German 2.6 Cologne engine - which had been bored out as far as it would go. Therefore the RS3100 used an overbored Essex 3 litre unit producing 148 bhp (although the racing engines were bored to 3421cc and produced around 415 bhp). The road going homologation RS3100's shared many fetures with the RS2600's; brakes, suspension, wheels bumpers, and headlights were all the same. The dummy side vents and interior were standard 3000GXL equipment but the 130mph speedometer, flat dish RS steering wheel, and AVO paint scheme were unique to the RS3100, as was an optional limmted slip differential.

Production ran from December 1973 to January 1974 and although 1000 cars were planned only 248 vehicles left the factory. These were launched into a country suffering from on oil crisis ; not the best market for a Capri with the largest engine ! At £2450.00 the RS3100 was nearly £800.00 more than a 3000E, and as the sales of the RS3100 were overhadowed by the launch of the MkII Capri in early 1974 in is no wonder that this car is one of the rarest going!

The Essex V6

The Ford Essex V6 engine was a 60c V6 engine built between 1966 and 1981 at the Dagenham, Essex, engine plant. It was produced in two main capacities, 2.5 litre and 3.0 litre, and was fitted to a wide range of vehicles, from Ford Transit vans to sports cars. It was the 3.1 litre version mentioned above that was produced for the 1973 Ford Capri RS 3100. The Essex V6 also formed the base for the 3.4 litre Cosworth GAA which, with the benefit of DOHC heads and fuel injection, generated 462 bhp (345 kW; 468 PS) at 9,000 rpm. This engine was used in the racing version of the Capri RS 3100, competing successfully in the European Touring Car Championship, as well as in Formula 5000 single-seaters.

The reason for the development was obvious. In 1973 Ford finished a very clear 2nd to BMW in the championship and kept on equal terms only by pushing the 2.9-litre engine so hard that it failed too often. The Ford engines with their Weslake alloy heads were giving about 320 bhp, whereas the BMW drivers had 375 bhp on tap from their larger engines. But Ford didn't wait to be beaten before deciding to get a new engine; they commissioned Cosworth to design the engine in 1972. The new engine was a typical Cosworth stock-block design: all the internals were specially made for racing, there were four valves per cylinder and the twin overhead camshafts per bank of cylinders were driven by toothed belts. Unusual features included the provision for three sparkplugs per cylinder and the use of butterfly throttle valves instead of slides.

Mike Hall

Mike Hall, who was closely involved in the design of the Chevy-Cosworth engine, was responsible for most of the design work on this engine too. Although he followed the Duckworth approach of installing four valves in a compact combustion chamber at a narrow included angle - 40 degrees in this case - he used a different construction for these heads. The head itself was fairly shallow and there was a separate carrier for each camshaft with separate covers. As a result, the appearance of the engine was quite different from that of the DFV Formula 1 engine, for example. Hall said that the heads were stiffer, machining was simpler, and "It looks like a racing engine anyway."

Because the 3.93-in. bores were so large - the stroke was only 2.85 in. - Hall thought they might encounter problems with too slow a flame speed, so he made provision for three sparkplugs for each cylinder. The three plugs could be installed in a row between the cam carriers. However, tests showed that although the use of three plugs altered the ignition timing it did not affect the power output, so only one central plug ended up being used. Not only were the camshafts belt driven, but so were almost all the auxiliaries. There was one belt for each bank of cylinders, one of which was tensioned by the water pump, which it also drove. A slim belt from the crankshaft also drove the scavenge oil pumps, and a toothed belt from one camshaft drove the Lucas fuel-injection metering unit.

By the early 1970s nearly all racing engines had slide throttles, so it was interesting to see that butterflies were used on this one. There were two reasons for this: first, on a 60-deg V-6 like this the air intakes would have needed to be downdraft if throttle slides were used. This would entail the use of inlet tracts that bent back on themselves. Second, throttle slides could easily get jammed with dust and dirt, which could waste time in a race and was downright dangerous anyway.